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  2. Small crustaceans in fresh waters
  3. Cladocera
  4. Chydoridae
  5. Alonella

Alonella exigua Fischer

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Alonella exigua is a littoral species which has a scattered distribution in Norway and it is not as common as A. excisa. The species occurs in water bodies of all sizes and in different stands of vegetation.

Key characteristics

: Alonella exigua.
| G.O. Sars

Alonella exigua (female)

: Alonella exigua.
| G.O. Sars

Alonella exigua (male)

Alonella exigua shows great similarities to A. excisa, but the polygons found in the structure of the shell of A. exigua do not have the small longitudinal lines inside. Furthermore its postabdomen is slightly shorter compared to A. excisa. The rostrum is relatively short and the ventral-posterior corner has a few small blunt denticles. The colour is grey or red-brown.

Female: Length 0.3–0.5 mm

Male: Length 0.2–0.3 mm

Ecology and distribution

A. exigua is not as common as A. excisa and is found in ca 12 % of the localities. It is a littoral species which has a scattered distribution in Norway. A. exigua is found between 5 and 1271 m a.s.l., and its frequency decreases both towards the sea level and towards the alpine zone, including a few records from above 1000 m a.s.l. The species occurs in water bodies of all sizes, in different stands of vegetation, and in water with pH varying between 3.9 and 9.0. Its frequency increases slightly when conductivity increases.

    pH
    Vitenskapelig navn < 4,5 4,5 - 4,9 5,0 - 5,4 5,5 - 5,9 6,0 - 6,4 6,5 - 7,0 7,0 - 7,4 > 7,5
    24 9,5 10,5 13,7 16 13,6 17,2 25,4
    Ledningsevne (m S/m)|Conductivity (m S/m)
    Vitenskapelig navn < 1,0 1,0 - 1,4 1,5 - 1,9 2,0 - 2,9 3,0 - 3,9 4,0 - 4,9 5,0 - 6,9 7,0 - 9,9 > 10,0
    3,3 8,3 12,8 12,4 13,7 19,1 19,4 23,1 22
    Innsjøareal (da)|Surface area (da)
    Vitenskapelig navn < 0,01 0,01 - 0,09 0,1 - 0,9 1,0 - 9,9 10,0 - 99 100 - 999 > 1000
    27,5 16,9 11,5 13,1 10,4 12,2 34,8
    Høyde over havet (moh.)|Elevation (m a.s.l.)
    Vitenskapelig navn < 100 100-299 300-499 500-699 700-999 >1000
    9,1 22,7 11 12,7 12,1 1,4

Look-alikes

Alonella excisa

: Alonella excisa.
Alonella excisa Fischer